Colon cancer is the second leading cause of cancer death among men and women in the United States. Many colon cancers could be prevented if precursor colonic polyps were detected and removed. In the last decade or so, computed tomographic (CT) and magnetic resonance (MR) colonography, two new “virtual” techniques for imaging the colon, have emerged as providing benefits over optical colonoscopies, the traditional standard for detecting and removing polyps. CT, MR, and other virtual colonography techniques take views through the abdomen using scanners, and then construct a three-dimensional model of the colon using computer software. The result is a set of images that provides a radiologist with a virtual view of the colon similar to what a gastroenterologist would see using an optical colonoscope. According to the National Cancer Institute and other well-known authorities on virtual colonography, advantages include that the techniques are relatively quick, fairly sensitive, and only minimally invasive.
As radiologists review the images of a virtual colonography procedure, they look for structures indicative of colonic polyps. Colonic residue (e.g. stool, fluid) structures may share many of the same characteristics of and often appear like colonic polyps in the imagery, especially in three-dimensional (i.e. volumetric) rendered images of the colon. Colonic residue also may obscure polyps from the view of the radiologist. For example, stool or fluid can partially or completely cover polyps. As a result, colonic residue may have a significant impact on the sensitivity with which radiologists detect cancerous polyps and properly diagnose a patient.
There have been numerous solutions proposed for addressing the problem of colonic residue in virtual colonography imagery. In the past, patients were asked to ingest a heavy laxative to remove all colonic residue from the colon prior to imaging. In response to complaints of discomfort expressed by patients, a minimal prep procedure was developed in which patients consumed an agent that tagged the colonic residue prior to imaging, causing the pixels or voxels of colonic residue to appear extremely bright on the rendered image(s) of the colon. Companies developed digital subtraction algorithms that electronically removed the tagged colonic residue from the image(s), presenting the radiologist with imagery in which the colonic residue has been replaced by air. Examples of digital subtraction algorithms can be seen in references such as U.S. Pat. No. 6,947,784; U.S. Patent Applications 20050107691, 200602158968, 20080027315, and 20080118133; and WO Application No. 2007030132. Unfortunately, in some cases, the agent may poorly tag the colonic residue and thus the digital subtraction algorithms may not effectively remove the residue from the imagery while leaving all other portions of the image. The algorithms may inadvertently remove or alter pixels or voxels of tissue-like regions in the image that include polyps and/or the colon wall. This may reduce the efficacy with which a radiologist detects and/or characterizes polyps and thus may reduce the accuracy with which the radiologist diagnoses a patient. Thus, many radiologists desire the flexibility to see the tagged colonic residue in the image in the event that what is tagged as colonic residue is actually a polyp. Thus, automatic electronic subtraction may provide an incomplete solution to the problem of colonic residue.
Rather than simply automatically electronically remove the identified colonic residue from the imagery, companies have turned their attention to computer-aided detection (CAD) algorithms as an automatic way of distinguishing polyps from colonic residue. Examples of CAD algorithms for detecting polyps in the presence of colonic residue can be seen in references such as U.S. Patent Application 20070071298, WO Application No. 2007064981, and “Automated detection of polyps with CT colonography: evaluation of volumetric features for reduction of false-positive findings,” Acad. Radiol., 2002; 9:386-97 by Nappi et al. While these algorithms may be effective, they do not operate at 100% sensitivity. Thus, such CAD algorithms may report false positives (that is, they may report a region as a polyp that is not one), fail to report true positives (that is, fail to report a true polyp), and rely on the radiologist to resolve these errors. More specifically, these CAD algorithms may misclassify polyps exhibiting colonic residue-like characteristics (e.g. tagged polyps, polyps obscured by stool, polyps that exist in regions of the colon having a high amount of colonic residue, etc.) as colonic residue. The CAD algorithms also may misclassify colonic residue exhibiting polyp-like characteristics (e.g. poorly tagged stool, stool obscuring polyps, etc.) as polyps.
The previously described approaches are all focused on detecting colonic residue for purposes of subtracting it from the colon imagery and/or improving the efficacy of automated polyp detection within the colon imagery. There is a need, however, for an alternative approach to dealing with colonic residue that overcomes the limitations of these approaches. In particular, there is a need for improved CAD algorithms to automatically detect colonic residue at a higher accuracy than prior art approaches for purposes of displaying the colonic residue to a radiologist. Such an approach could help the radiologist to better distinguish colonic residue from polyps in medical images of the colorectal region, thus improving the quality of patient diagnosis and treatment.
It is therefore an object of this disclosure to assist a radiologist in identifying polyps by automatically detecting and outputting regions of colonic residue in medical imagery of the colon.